In secure applications performed by electronic circuits it is common to provide output data in an encrypted form to hinder the ability of a rival eavesdropper from collecting the data in an easily usable form. Additionally secure electronic circuits may be robustly packaged so that the rival eavesdropper cannot readily access the silicon elements of the circuit and attach snooping equipment to the inputs and/or outputs of the silicon elements that compose the circuit.
If the rival eavesdropper has physical access and enough time he may be able to uncover internal connections of the circuit and access data before it is encrypted for output. Optionally, the snooping equipment may be attached in parallel to a connection or may be inserted in series with the other elements of the circuit.
To overcome this problem in some circuits the silicon elements encrypt data exiting from the element so that the rival eavesdropper will not be able to collect unencrypted data from connections within the electronic circuit even when gaining access to the outputs of elements.
In any case transmitting data in an encrypted form between circuit elements has a price. Each element needs to have a built in encryption circuit and/or an un-encryption circuit embedded therein to support such an option.